This application claims the benefit of Korean Patent Application No. 1999-61337, filed Dec. 23, 1999 and Korean Patent Application No. 2000-12056, filed Mar. 10, 2000, the disclosures of which are hereby incorporated herein by reference.
The present invention relates generally to chemical vapor deposition (CVD) and, more particularly, to forming ruthenium films by CVD and ruthenium films and integrated circuit devices formed thereby.
Noble metals, such as ruthenium (Ru), platinum (Pt), iridium (Ir) and osmium (Os), have traditionally been used infrequently in semiconductor integrated circuits. Recently, however, these noble metals and/or the oxidized substances thereof have been studied for potential use as a lower or upper electrode of a capacitor. This is because the desired electrical characteristics for a capacitor may not be attainable by using polysilicon, which is commonly used as an electrode material when a material, such as Ta2O5, BST ((Ba, Sr)TiO3) or PZT((Pb, Zr)TiO3), that has a high dielectric constant is used as a dielectric film. Because Ru has a generally good leakage current characteristic and may be etched more easily than Pt, attention has been focused on the use of Ru film as the electrode of a capacitor.
Traditionally, sputtering methods have been used to form Ru films. In accordance with conventional sputtering methods, a Ru film may be densely formed and a generally good surface morphology may be achieved, thereby obtaining a Ru film having a generally good leakage current characteristic and a generally good resistance characteristic. One disadvantage to conventional sputtering methods, however, is that the Ru films formed thereby may provide poor step coverage. As a result, sputtering methods may be less desirable when forming an electrode having a three-dimensional shape, such as a cylinder shape or a fin shape.
CVD has been proposed for forming Ru films because films formed by CVD generally have better step coverage than those formed by sputtering methods. Specifically, in conventional CVD methods, Ru is deposited on a substrate or an interlayer dielectric layer using a vaporized Ru source gas and a reactant gas (i.e., a catalyzer) so that generally good step coverage can be achieved. Unfortunately, the surface morphology of a Ru film formed by CVD is typically worse than that of a Ru film formed by conventional sputtering methods. As a result, it may be difficult to obtain desired leakage current and resistance characteristic using conventional CVD methods. Consequently, there exists a need for improved CVD methods for forming Ru film.
According to embodiments of the present invention, a ruthenium (Ru) film is formed on a substrate as part of a two-stage methodology. During the first stage, the Ru film is formed on the substrate in a manner in which the Ru nucleation rate is greater than the Ru growth rate. During the second stage, the Ru film is formed on the substrate in a manner in which the Ru growth rate is greater than the Ru nucleation rate. When the Ru film is formed in a manner such that the nucleation rate is greater than the growth rate, the density and uniformity of the Ru grains in the film may be enhanced, which may provide a smooth surface morphology. When the Ru film is formed in a manner such that the growth rate is greater than the nucleation rate, the Ru grains in the film may grow substantially uniformly in various directions, but the nuclei may not be densely formed. As a result, the sheet resistance of the Ru film may be reduced. Moreover, the smooth surface morphology of the Ru film formed during the initial deposition stage may advantageously facilitate the formation of a continuous Ru film in the second deposition stage. Thus, a Ru film formed in accordance with embodiments of the present invention may be viewed as comprising two portions: a first portion having relatively densely formed nuclei having a relatively smooth surface morphology and a second portion having relatively sparsely formed nuclei. The relatively smooth surface morphology of the Ru film formed during the first deposition stage may facilitate the formation of a continuous Ru film during the second deposition stage and the relatively sparsely formed nuclei of the Ru film formed during the second deposition stage may provide for improved electrical characteristics in the form of reduced sheet resistance.
In further embodiments of the present invention, a Ru film is formed on a substrate by chemical vapor deposition (CVD) using a Ru source gas and oxygen as a reactant gas. During the formation of the ruthenium film on the substrate by CVD, one or more of the following process conditions are changed: the CVD chamber pressure, the oxygen gas flow rate, and the substrate temperature. For example, in particular embodiments of the present invention, the CVD chamber pressure may be decreased, the oxygen gas flow rate may be decreased, and/or the substrate temperature may be increased during the deposition of the Ru film. While the CVD chamber pressure and the oxygen gas flow rate are relatively high and the substrate temperature is relatively low, the Ru film may be formed with relatively dense nuclei so that a relatively smooth surface morphology may be achieved. Conversely, while the CVD chamber pressure and/or the oxygen gas flow rate are relatively low and/or the substrate temperature is relatively high, the Ru film may be formed with relatively sparsely formed nuclei for reduced sheet resistance. Thus, by changing any or all of the three process conditions corresponding to the CVD chamber pressure, the oxygen gas flow rate, and the substrate temperature, the physical and electrical characteristics of the Ru film may be varied.
In still further embodiments of the present invention, a two-step methodology may be used to form a Ru film. For example, in a first step, a Ru film may be formed on a substrate by CVD using a Ru source gas and oxygen as a reactant gas at a first CVD chamber pressure and first oxygen gas flow rate. In a second step, the Ru film is formed on the substrate by CVD using the Ru source gas and oxygen as a reactant gas at a second CVD chamber pressure and second oxygen gas flow rate. Importantly, however, either or both of the second CVD chamber pressure and second oxygen flow rate are less than the first CVD chamber pressure and first oxygen flow rate, respectively.
In particular embodiments of the present invention, the first CVD chamber pressure is in a range from about 10 Torr to 50 Torr, the second CVD chamber pressure is in a range from about 0.05 Torr to 10 Torr, the first oxygen flow rate is in a range from about 500 sccm to 2000 sccm, and the second oxygen flow rate is in a range from about 10 sccm to 300 sccm.
In still further embodiments of the present invention, the substrate temperature is in a range from about 250xc2x0 C. to 450xc2x0 C. during both steps of the two-step methodology for forming the Ru film. In other embodiments of the present invention, however, the substrate temperature is about 10xc2x0 C. to 30xc2x0 C. higher when performing the second step of the two-step methodology than it is when performing the first step of the two-step methodology.
In yet further embodiments of the present invention, the Ru film may be heat treated at about 250xc2x0 C. to 450xc2x0 C. in an atmosphere comprising oxygen or ozone after the first step of the two-step methodology and/or after completing both steps of the two-step methodology.
In other embodiments of the present invention, integrated circuit devices, such as capacitors, may be formed by forming a lower and/or an upper electrode as a Ru film as described in the foregoing.
Thus, in summary, the present invention may be used to form Ru films by changing at least one process condition during the CVD methodology. As a result, Ru films having improved continuity and reduced sheet resistance may be obtained.